A great variety of methods and systems have been developed for direct optical measurement of teeth and the subsequent automatic manufacture of dentures. The term “direct optical measurement” signifies surveying of teeth in the oral cavity of a patient. This facilitates the obtainment of digital constructional data necessary for the computer-assisted design (CAD) or computer-assisted manufacture (CAM) of tooth replacements without having to make any cast impressions of the teeth. Such systems typically include an optical probe coupled to an optical pick-up or receiver such as charge coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) sensor and a processor implementing a suitable image processing technique to design and fabricate virtually the desired product.
One type of system that performs intra-oral scans is a system that uses confocal imaging to image a three dimensional surface. Such systems that use confocal imaging typically include field lenses to flatten an imaging field and enable flat focal planes for emitted light beams. Such flat focal planes ensure that the surface topology of scanned three dimensional surfaces is accurate. However, the field lenses are diverging lenses that open the rays of the light beams. This causes the optics of the confocal imaging apparatus to be enlarged. Additionally, the field lenses should be aligned to ensure accuracy. Such alignment can be a time consuming and challenging process.